Elsevier

Materials Letters

Volume 78, 1 July 2012, Pages 54-57
Materials Letters

Enhanced electrical conductivity of sodium polyacrylate encapsulated multi-walled carbon nanotubes

https://doi.org/10.1016/j.matlet.2012.03.062Get rights and content

Abstract

Multi-walled carbon nanotubes (MWNTs) were grafted with poly (acrylic acid) (PAA) forming PAA-g-MWNTs, which were subsequently neutralized with a sodium hydroxide solution resulting in sodium polyacrylate encapsulated MWNTs (PAANa-g-MWNTs). Then PAANa-g-MWNTs were introduced into polyetherimide (PEI) as an electrically conductive additive. The polymer-encapsulated MWNTs could be finely dispersed in the PEI matrix. Moreover, determinations of the electrical conductivity and electrochemical impedance spectra (EIS) of the nanocomposites indicated that the electrical conductive percolation threshold of PAANa-g-MWNTs in PEI was decreased obviously over that of pristine MWNTs, and partially because of the improved dispersion of the conductive filler, partially because of the joint efforts of the moderate ionic conductivity induced by PAANa with the electronic conductivity by MWNTs in the polymer matrix.

Highlights

► PAANa-g-MWNTs were introduced into PEI as an electrically conductive additive. ► The percolation threshold was decreased from 4% of MWNTs to 1.75% of PAANa-g-MWNTs. ► The enhanced conductivity came from ionic conducting mechanism induced by PAANa.

Introduction

Being a high performance thermoplastic, polyetherimide (PEI) has been widely used in medical and chemical instrumentation, electrical equipment, and automobile parts due to their high mechanical properties and superior thermal stability. Unfortunately, PEI is electrically non-conductive and easy to accumulate electrostatic charges in the application fields of electrical equipment, such as computer hardware and electronic circuits. The electrostatic discharge would cause a permanent damage of electrical devices. Consequently, to enhance electrical conductivity of PEI constituted one of major research interests [1], [2], [3], [4].

Carbon nanotubes (CNTs) have been considered as a promising candidate of conductive additives because of their extraordinary electrical conductivity and unique length-to-diameter ratio [5]. In order to fully exploit the conductive properties of CNTs, it was well known that proper surface modification, which was usually achieved by using dispersing agents [6] and various chemical functionalizations [7], [8], is necessary to avoid serious aggregation of CNTs and improve the dispersion of CNTs in polymeric matrix. However, the strong oxidation treatment necessary for the surface functionalization may destroy or shorten CNTs, which seriously damaged their electrical conductivity and mechanical strengths [9].

In this work, we used in-situ free radical polymerization in a poor solvent to encapsulate poly (acrylic acid) (PAA) chains onto the surface of multi-walled carbon nanotubes (MWNTs). Subsequently, the encapsulated PAA were transformed to sodium polyacrylate (PAANa) in a sodium hydroxide solution. PAANa complex is a typical ionic polymer in which Na+ ions are mobile around the backbone of polymer. Since the acidamide groups in PEI could strongly interacted with the carboxylate in PAANa, a good compatibility between PEI and the PAANa encapsulated MWNTs (PAANa-g-MWNTs) could be expected. Furthermore, ionic-transport mechanism induced by PAANa was also introduced, and then the electrical conductivity of PEI/PAANa-g-MWNT nanocomposites was enhanced.

Section snippets

Materials

MWNTs (purity > 95%, diameter 10–30 nm and length 0.5–500 μm) were provided by Shenzhen Nanotech port, China. Acrylic acid (AA) was purchased from Tianjin Fuchen Chemical Reagent Co. Ltd. 2,2′-azoisobutyrontrile (AIBN) was provided by Vas Chemical of China. Sodium hydroxide, acetone and N-methyl-2-pyrrolidone (NMP) were supplied by Beijing Modern Eastern Fine Chemical Co. Ltd. Acetone was distilled for purification before use.

Preparation of PAANa-g-MWNTs

0.1 g MWNTs and 1 g AA were dispersed into 100 mL acetone in a flask by

Results and discussion

Fig. 1 showed the FTIR spectra of PAA, PAA-g-MWNTs, and PAANa-g-MWNTs. The absorption peaks in the range of 1627–1711 cm 1 were assigned to carbonyl groups, and the shift could be attributed to a strong interaction between PAA and MWNTs. The peaks in the 2805–2960 cm 1 region were assigned to the C–H stretch vibration of PAA backbone. The peak at 1560 cm 1 corresponded to the IR active phonon mode of MWNTs [10]. In addition, a broad absorption band in the region of 3100–3600 cm 1 in PAANa-g-MWNTs

Conclusions

A highly conductive PEI/PAANa-g-MWNT nanocomposite was prepared with a simple method. The encapsulation of PAANa on MWNTs enhanced the compatibility between MWNTs and PEI matrix and a better dispersion of MWNTs was observed. Compared with pristine MWNTs, the percolation threshold of MWNTs was decreased from 4% to 1.75%. The impedance diagrams demonstrated that the introduction of PAANa-g-MWNTs induced another conducting mechanism—ionic conductivity in the system and thus enhanced the

Acknowledgments

This work was supported by the 13th CHINA-JAPAN S & T Cooperation (2010DFA52070).

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